CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Current Assets:
Cash	$ 36,469	$ 38,703
Receivables, Net	903,578	856,346
Unbilled Revenues	205,155	211,758
Taxes Receivable	117,792	337,307
Fuel, Materials and Supplies	289,561	349,664
Regulatory Assets Current	709,660	672,493
Marketable Securities - Current	124,830	124,173
Prepayments and Other Current Assets	62,884	102,021
Total Current Assets	2,449,929	2,692,465
Property, Plant and Equipment, Net	19,079,189	18,647,041
Deferred Debits and Other Assets:
Regulatory Assets Long Term	4,016,684	4,054,086
Goodwill	3,519,401	3,519,401
Marketable Securities	497,919	515,025
Other Long-Term Assets	316,817	349,957
Total Deferred Debits and Other Assets	8,350,821	8,438,469
Total Assets	29,879,939	29,777,975
Current Liabilities:
Notes Payable	953,700	956,825
Long-Term Debt - Current Portion	278,883	245,583
Accounts Payable - Current	598,716	868,231
Regulatory Liability Current	208,510	235,022
Deferred Tax Liabilities Current	203,375	160,288
Other Liabilities - Current	595,801	668,432
Total Current Liabilities	2,838,985	3,134,381
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	4,606,159	4,467,473
Regulatory Liabilities Long-Term	510,807	515,144
Long-Term Derivative Liabilities	380,966	409,632
Accrued Pension, SERP and PBOP	1,636,769	1,638,558
Other Long-Term Liabilities	875,985	874,387
Total Deferred Credits and Other Liabilities	8,010,686	7,905,194
Capitalization:
Long-Term Debt	8,689,647	8,606,017
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,568	155,568
Common Shareholders' Equity:
Common Stock	1,669,167	1,666,796
Capital Surplus, Paid In	6,253,411	6,235,834
Retained Earnings	2,644,485	2,448,661
Accumulated Other Comprehensive Loss	(72,033)	(74,009)
Treasury Stock	(309,977)	(300,467)
Common Shareholders' Equity	10,185,053	9,976,815
Total Capitalization	19,030,268	18,738,400
Total Liabilities and Capitalization	29,879,939	29,777,975
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	9,227	2,356
Receivables, Net	395,863	355,140
Accounts Receivable from Affiliated Companies	22,981	16,757
Unbilled Revenues	103,767	102,137
Taxes Receivable	0	116,148
Regulatory Assets Current	263,713	220,344
Materials and Supplies	50,357	46,664
Prepayments and Other Current Assets	15,043	37,822
Total Current Assets	860,951	897,368
Property, Plant and Equipment, Net	6,934,618	6,809,664
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,461,483	1,475,508
Other Long-Term Assets	146,299	177,568
Total Deferred Debits and Other Assets	1,607,782	1,653,076
Total Assets	9,403,351	9,360,108
Current Liabilities:
Notes Payable To Affiliated Companies	85,600	133,400
Long-Term Debt - Current Portion	0	162,000
Accounts Payable - Current	208,860	272,971
Accounts Payable to Affiliated Companies	58,227	65,594
Obligations to Third Party Suppliers	67,844	73,624
Regulatory Liability Current	122,617	124,722
Deferred Tax Liabilities Current	46,811	34,073
Derivative Liabilities - Current	90,933	88,459
Other Liabilities - Current	97,062	119,347
Total Current Liabilities	777,954	1,074,190
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,666,607	1,642,805
Regulatory Liabilities Long-Term	71,245	81,298
Long-Term Derivative Liabilities	380,196	406,199
Accrued Pension, SERP and PBOP	286,131	273,854
Other Long-Term Liabilities	144,983	148,844
Total Deferred Credits and Other Liabilities	2,549,162	2,553,000
Capitalization:
Long-Term Debt	2,975,091	2,679,951
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	116,200	116,200
Common Shareholders' Equity:
Common Stock	60,352	60,352
Capital Surplus, Paid In	1,805,638	1,804,869
Retained Earnings	1,119,702	1,072,477
Accumulated Other Comprehensive Loss	(748)	(931)
Common Shareholders' Equity	2,984,944	2,936,767
Total Capitalization	6,076,235	5,732,918
Total Liabilities and Capitalization	9,403,351	9,360,108
NSTAR Electric Company [Member]
Current Assets:
Cash	2,848	12,773
Receivables, Net	288,581	234,481
Accounts Receivable from Affiliated Companies	50,582	40,353
Unbilled Revenues	41,294	29,741
Taxes Receivable	43,940	144,601
Fuel, Materials and Supplies	56,584	74,179
Regulatory Assets Current	258,489	198,710
Prepayments and Other Current Assets	3,870	10,815
Total Current Assets	746,188	745,653
Property, Plant and Equipment, Net	5,451,668	5,335,436
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,198,167	1,179,100
Other Long-Term Assets	58,936	73,051
Total Deferred Debits and Other Assets	1,257,103	1,252,151
Total Assets	7,454,959	7,333,240
Current Liabilities:
Notes Payable	377,200	302,000
Long-Term Debt - Current Portion	200,000	4,700
Accounts Payable - Current	173,863	217,311
Accounts Payable to Affiliated Companies	71,066	63,517
Renewable Portfolio Standards Compliance Obligation	61,200	35,698
Regulatory Liability Current	5,007	49,611
Deferred Tax Liabilities Current	107,995	55,136
Other Liabilities - Current	86,718	115,991
Total Current Liabilities	1,140,118	878,788
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,538,988	1,527,667
Regulatory Liabilities Long-Term	266,572	262,738
Accrued Pension, SERP and PBOP	220,000	235,529
Other Long-Term Liabilities	123,421	129,279
Total Deferred Credits and Other Liabilities	2,148,981	2,155,213
Capitalization:
Long-Term Debt	1,592,722	1,792,712
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000	43,000
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	995,378	994,130
Retained Earnings	1,534,500	1,468,955
Accumulated Other Comprehensive Loss	260	442
Common Shareholders' Equity	2,530,138	2,463,527
Total Capitalization	4,165,860	4,299,239
Total Liabilities and Capitalization	7,454,959	7,333,240
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	818	489
Receivables, Net	84,607	80,151
Accounts Receivable from Affiliated Companies	4,290	3,194
Unbilled Revenues	36,472	40,181
Taxes Receivable	34,985	14,571
Fuel, Materials and Supplies	137,119	148,139
Regulatory Assets Current	88,773	111,705
Prepayments and Other Current Assets	23,538	27,821
Total Current Assets	410,602	426,251
Property, Plant and Equipment, Net	2,714,915	2,635,844
Deferred Debits and Other Assets:
Regulatory Assets Long Term	282,215	293,115
Other Long-Term Assets	34,083	39,228
Total Deferred Debits and Other Assets	316,298	332,343
Total Assets	3,441,815	3,394,438
Current Liabilities:
Notes Payable To Affiliated Companies	133,500	90,500
Accounts Payable - Current	69,884	93,349
Accounts Payable to Affiliated Companies	22,201	33,734
Regulatory Liability Current	5,602	16,044
Deferred Tax Liabilities Current	35,963	36,164
Other Liabilities - Current	30,605	38,969
Total Current Liabilities	297,755	308,760
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	632,890	587,292
Regulatory Liabilities Long-Term	50,250	51,372
Accrued Pension, SERP and PBOP	99,318	93,243
Other Long-Term Liabilities	50,054	50,155
Total Deferred Credits and Other Liabilities	832,512	782,062
Capitalization:
Long-Term Debt	1,076,319	1,076,286
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	748,635	748,240
Retained Earnings	493,449	486,459
Accumulated Other Comprehensive Loss	(6,855)	(7,369)
Common Shareholders' Equity	1,235,229	1,227,330
Total Capitalization	2,311,548	2,303,616
Total Liabilities and Capitalization	3,441,815	3,394,438
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	1,143	0
Receivables, Net	61,491	51,066
Accounts Receivable from Affiliated Companies	5,507	7,851
Unbilled Revenues	15,912	15,146
Taxes Receivable	1,148	18,126
Regulatory Assets Current	54,926	51,923
Marketable Securities - Current	38,441	28,658
Prepayments and Other Current Assets	5,496	7,607
Total Current Assets	184,064	180,377
Property, Plant and Equipment, Net	1,508,207	1,461,321
Deferred Debits and Other Assets:
Regulatory Assets Long Term	138,138	146,307
Marketable Securities	19,809	29,452
Other Long-Term Assets	27,147	22,018
Total Deferred Debits and Other Assets	185,094	197,777
Total Assets	1,877,365	1,839,475
Current Liabilities:
Notes Payable To Affiliated Companies	60,600	21,400
Long-Term Debt - Current Portion	50,000	50,000
Accounts Payable - Current	36,327	53,732
Accounts Payable to Affiliated Companies	10,217	14,328
Regulatory Liability Current	16,847	22,486
Deferred Tax Liabilities Current	20,822	18,089
Other Liabilities - Current	24,608	24,080
Total Current Liabilities	219,421	204,115
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	422,502	416,822
Regulatory Liabilities Long-Term	12,921	10,835
Accrued Pension, SERP and PBOP	19,530	17,705
Other Long-Term Liabilities	38,065	33,747
Total Deferred Credits and Other Liabilities	493,018	479,109
Capitalization:
Long-Term Debt	578,007	578,471
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	391,398	391,256
Retained Earnings	187,673	178,834
Accumulated Other Comprehensive Loss	(3,018)	(3,176)
Common Shareholders' Equity	586,919	577,780
Total Capitalization	1,164,926	1,156,251
Total Liabilities and Capitalization	$ 1,877,365	$ 1,839,475